This invention relates to devices, implants and prostheses used in orthopaedic surgery, and, more particularly, to bone plates used to reinforce fractured or osteotomically separated bones and thus promote healing.
A compressive screw system, also known as the DCS system, is a bone plate system that has been used in trauma surgery for many years. The procedures for use of this system are well documented by the AO Institute, an institute having as one of its goals, the promotion of new orthopaedic surgical procedures. This system included a bone plate having slots communicating therethrough. A land in which the slot is wider at one end defines a stepped surface adjacent the portion of the slot that extends through the bone plate. The stepped surface is generally cut with a spherical endmill, thus creating a spherical stepped surface.
In a still further development, bone plates have been developed having individual threaded apertures and non-threaded apertures interspersed along the length of the plate. In this and other designs, the distance between holes has become a standard. Although an improvement over the inserts noted above, the locking positions are pre-defined, and only available in limited locations, which also reduce surgical flexibility. In another product variation, expandable, lockable inserts enter into the slots of a standard bone plate. When the bone screw passes through one of these inserts and is torqued down, the insert expands and locks the screw in place. However, this insert is locked in a secondary operation. This is not desirable because this requires more operating room time and adds complexity to the procedure. Further, the inserts must be added in the specific location before the plate is fixed to the bone and cannot be subsequently inserted. This limits the choice of placement during surgery if the need arises.
Also, the above insert designs rely on a friction lock via contact between two surfaces. Friction locks are not reliable and come lose more easily than threaded locked holes. The result of such a design is inferior to that of the threaded plate and screw designs discussed below.
In U.S. Pat. No. 5,002,544, there is shown an osteosynthetic pressure plate having a cross-section transverse to the longitudinal axis of the plate at at least one point being wider toward the upper surface than toward the lower surface and the plate having recesses in the lower surface so that upon application to a bone there is space between the bone and the plate. The cross-section between the screw holes is reduced, preferably to the extent that the resistance of the plate to bending in this area is less than in the area of the holes. Because of the reduced bend resistance between the holes, the plate can more easily be adapted to conform to the anatomy of the bone. Furthermore, this can be done without deformation of the holes, thus minimizing the resulting loss of fatigue strength and minimizing the misfit of the screw heads.
Further, U.S. Pat. No. 5,709,686 describes a bone plate that has recesses or reduced thickness portions on its sides, between threaded apertures. Although the purpose is not specifically described, these recesses appear to function to avoid warpage of the threaded portions when the bone plate is bent. However, when such a bone plate is fixed to a bone, these discontinuous recesses are exposed and may potentially come into contact with and potentially aggravate muscle tissue.
Still further, U.S. Pat. No. 5,733,287 shows, in FIG. 4, a plate that has transverse cuts 13 and a longitudinal cut 14 on the lower surface 7 to reduce contact between the plate and bone. Due to the transverse undercuts 13, the cross-section 15 between the holes is already significantly reduced and therefore is not further decreased by an additional groove 10 on the upper surface 6 as in the embodiment according to FIG. 3. To avoid a cross-section that is too thin, the groove 10 on the upper surface 6 is made discontinuous in short segmental grooves 16 providing a smooth transition into and out of the holes 8.
In yet another solution, PCT application no. WO01/54601 combines the features of the DCS system discussed above with a locking screw. Such a system is known as the combi-slot. In this design, the stepped surface of the slot is generally ramped or tapered so as to be deeper at one end than at another. This enables the positioning and selective fixing of the bone plate for compressing two bone fragments together with a preload created by wedging action. In this manner, the bones are placed in a position that the surgeon believes would best promote healing.
Further, this combi-hole includes two distinct overlapping portions in a single slot. One portion of the slot is suited to receive a standard bone screw, while the other portion of the slot is suited to receive a threaded peg oriented perpendicular to the top surface of the bone plate. Also, the combi-holes are generally oriented with the threaded portions being on the innermost end of the combination and the unthreaded portions oriented toward the ends of the bone plate. This improvement increased the flexibility of choice available to orthopedic surgeons using the device in that it was more likely that a hole would be present at a suitable anchoring point in the bone plate. Nevertheless, there are often trauma situations that are best served by the threaded portion being at the extreme ends of the bone plate and/or at various positions throughout the plate. In addition, sometimes there is no specific center of the fracture in such a situation, use of the combi-hole design is limited.
While patent application no. WO01/54601 has proven advantageous because screws can be locked to the plate, the presence of an unthreaded slot limits the user's ability to have multiple orientations for the screw.
In a further development, the AO Institute has studied and proposed the use of endpegs which are rigidly fixed in the extreme ends of the bone plate. Such an arrangement has been shown to better resist the flexing of the bone than use of a bone screw alone. Flexing can otherwise loosen the connection between the bone plate and bone in other bone plate systems.
U.S. Pat. No. 5,324,290 shows a complex bone plate having slots with countersunk circular recessed cut at intervals along the slot (a similar arrangement is shown in U.S. Pat. No. 4,696,290). It further shows the bone plate torqued against the bone so as to at least marginally, conform to the shape of the bone (see FIG. 2). Other patents of interest include U.S. Pat. Nos. 3,716,050, 3,659,595, 5,681,311, 5,261,910, and 5,364,399, as well as German Patent application DE4341980A1, all showing combinations of conventional slots and recesses which do not fully accommodate a bone screw having a threaded head.
In comparison with the combi-hole design and the friction locking design described above, what is needed is a bone plate that provides greater flexibility of choice to the surgeon. More specifically, what is needed is a bone plate that provides this choice of plate placement while reliably and permanently fixing the bone plate to the bone fragments, in any hole position.
What is needed is a bone plate that provides greater flexibility of choice to the surgeon, in a bone plate that has multiple orientations for the locking screw and thus, plate placement, while reliably and permanently fixing the bone plate to the bone fragments, in any hole position.
More specifically, what is needed is a bone plate that provides this choice while reliably and permanently fixing the bone plate to the bone fragments or osteotomically separated bone portions.
In addition, what is needed is a versatile bone plate having recesses which determine where the bone plate will bend, in order to avoid the threads in any holes to be bent or warped, while maintaining a smooth external surface.
Finally, what is needed is a bone plate with holes that create bi-directional compression.